This invention relates to a process of making colored finely divided opaque particles based on aminoformaldehyde resin having high surface area and being suitable as pigments in the fields of plastic, rubber, paint, paper coating and printing ink.
Processes for producing finely divided polymeric particles by adding a curing catalyst such as sulfuric acid to an aqueous solution of amino resin obtained by reacting urea or melamine with formaldehyde and then curing the resin with stirring, have been known in the past [GB 672763, GB 748484, U.S. Pat. No. 2,851,424]. However, these known processes possessed a number of shortcomings, since the amino-formaldehyde resin would rapidly harden in the presence of the curing catalyst to become insoluble and infusible. For instance, in these processes it is necessary to conduct the hardening reaction under strictly controlled conditions for obtaining a finely divided resin having a uniform particle size. Further, when it is intended to produce colored finely divided polymeric particles, there are imposed several restrictions like the class of dye that can be used and the time of its use in the case of the conventional processes, it being possible to obtain colored finely divided hardened resins only by adding water-soluble dyes when the amino resin is in an aqueous solution state and then hardening the resin.
Relatively recently, a number of approaches to improve the process of making finely divided polymeric particles has been disclosed. One approach entails the use of protective colloids, like water-soluble polymers which greatly increase the viscosity of aqueous solutions and make the hardening of the amino-formaldehyde resin more controllable [U.S. Pat. No. 3,981,845]. This method was used for making a highly dispersed insoluble and infusible urea-formaldehyde polymer having a specific surface area of more than 10 square meters per gram and an average particle size smaller than 5 microns.
The second approach includes the stage of formation of a water-in-oil emulsion when a water solution of urea-formaldehyde prepolymer is admixed with high shear to a non-solvent, like xylene [U.S. Pat. No. 3,928,272]. This process has been used for preparation of particles with an average diameter from 0.2 to 4 microns and a specific surface area up to 90 square meters per gram. A dispersing agent, like potassium tripolyphosphate, sodium hexamethaphosphate or sodium laurylsulfate is added to prevent the particles from clustering.
A third approach involves the preparation of a soluble and fusible aminoformaldehyde resin by reacting benzoguanamine or its mixture with melamine and formaldehyde in an aqueous medium, introducing this aqueous liquid to an aqueous solution of protective colloid with stirring to prepare a microemulsion, and adding a curing catalyst to said emulsion [U.S. Pat. Nos. 3,945,980, 4,069,176].
All three approaches lead to microspheres of mainly spheroidal shape consisting of crosslinked amino-formaldehyde polymer with an average particle size smaller than 5 microns. Because of the approximately spherical shape of the polymer particles having a substantially uniform size, the level of opacity of said products is limited.
In the present invention, a high degree of opacity is achieved with particles of an irregular shape of crosslinked amino-formaldehyde resin having high surface area and an average particle size below 1 micron. In addition, the level of opacity can be monitored and the shape (spherical or irregular) of particles changed, depending on the presence of surfactants (dispersing agents).
The instant invention provides novel highly dispersed particles of solid insoluble and infusible amino-formaldehyde condensation polymer in the form of a fluffy bright colored powder, said product having a specific surface area of more than 100 square meters per gram, said product essentially consisting of non-spherical microparticles having substantially uniform size and irregular shape (if no surfactants are used) or mainly spherical microparticles having mainly submicron size: up to 70% below 0.7 microns and up to 40% below 0.5 microns (if a surfactant or a mixture of surfactants are used).
A process for producing such finely divided particles in colored form comprises the steps of reacting in aqueous medium at a pH of 6-9 a member selected from the group consisting of either urea or benzoguanamine and a mixture of 100-0% by weight of urea and 0-100% by weight of benzoguanamine with formaldehyde in a ratio of 1 mol of the former to 1.3-3 moles of the latter to prepare an aqueous liquid of a soluble and fusible prepolymer, introducing this water-containing prepolymer into an organic solvent with boiling point below 80xc2x0 C. and completely mixable with the water in a ratio of 70-30% by weight of prepolymer and 30-70% by weight of organic solvent, dyeing said mixture with a single fluorescent dye or a combination of several dyes, introducing with high shear the dyed resin-containing mixture in to an aqueous solution of protective colloid consisting o f 92-98.5 % of water, 1-3% of water-soluble polymer, 0-3% of a nonionic surfactant or a mixture of non-ionic and ionic surfactants and 0.5-2.0% of acidic curing catalyst at a reaction temperature in the range from 70-100xc2x0 C., and thereafter separating the hardened resin from the suspension followed by drying and deaggregating the dried hardened resin.
The dyed finely divided particles can be obtained in accordance with the present invention in the following manner. Either urea or benzoguanamine or a mixture of 100-0% by weight of urea and 0-100% by weight of benzoguanamine and 1.3-3 moles, preferably 1.5-2.5 moles, per mole thereof of formaldehyde are reacted at a pH range of 6-9, and preferably 7-8.5, and suitably a temperature in the range of 50-95xc2x0 C., preferably 70-90xc2x0 C. using water as the reaction medium to prepare an aqueous solution of a soluble and fusible prepolymer. The reaction time should appropriately be so long that the greater part of formaldehyde (about 90%) has the opportunity of reacting with either urea or benzoguanamine, but not so long that the molecular weight of the prepolymer becomes so high that it can not be homogeneously mixed with water-mixable organic solvent. Typical representatives of organic solvents are aliphatic ketones and alcohols, like acetone, methylethylketone, methanol or ethanol. The concentration of either urea or benzoguanamine or a mixture thereof and formaldehyde are selected so that the concentration of the prepolymer is in the optimum range of 20-35%, preferably 25-30% by weight.
Appropriately, the organic solvent is added to the prepolymer at a temperature in the range of 40-60xc2x0 C. in a ratio of 70-30% by weight of prepolymer and 30-70% by weight of organic solvent. A ratio between the prepolymer and organic solvent is selected preferably so that complete solubility of fluorescent dyes in said mixture can be achieved. In the case where a water-soluble dye is used, a ratio of 70-50% by weight of prepolymer and 30-50% by weight of organic solvent is recommended. In the case where an oil-soluble (water-insoluble) dye is used, a ratio of 50-30% by weight of prepolymer and 50-70% by weight of organic solvent is recommended.
Appropriately, the typical representatives of water-soluble dyes are rhodamines, fluoresceines and some coumarins, containing ionic groups in their structure, like Basic Yellow 40. The typical representatives of oil-soluble (water-insoluble) dyes are coumarins, like Blankophor SOL, Solvent Yellow 135, naphthalimides and non-fluorescent polymer-soluble dyes, like heterocyclic compounds with structures I-IX or a combination of the above mentioned dyes in a ratio of 10-90% by weight of fluorescent dyes and 90-10% by weight of dye with structure (I)-(IX). 
wherein
R1 and R2 are identical or different and are hydrogen, C1-6alkyl, C6-10aryl, (C6-10)aryl-(C1-6)alkyl or (C1-6)alkyl-(C6-10)aryl, it being possible for the alkyl and/or aryl radicals to be substituted by hydroxyl, C1-6alkoxy, C6-10aryloxy or halogen; and
X is 
xe2x80x83wherein
R3 is is hydrogen, halogen, xe2x80x94NR4R6, R6xe2x80x94Oxe2x80x94 or R6xe2x80x94Sxe2x80x94, in which R6 is C1-6alkyl, C6-10aryl (C6-10)aryl-(C1-6)alkyl or (C1-6)alkyl-(C6-10)aryl, in which the alkyl and/or aryl radicals can be substituted by hydroxyl, C1-6alkoxy, C6-10aryloxy or halogen; and R4 is hydrogen, C1-6alkyl, C6-10aryl, (C6-10)aryl-(C1-6)alkyl or (C1-6)alkyl-(C6-10)aryl, it being possible for the alkyl and/or aryl radicals to be substituted by hydroxyl, C1-6alkoxy, C6-10aryloxy or halogen; and
Y is sulphur, oxygen or Nxe2x80x94R4, in which R4 has the meaning given above. 
wherein R3 and have the meanings given above; and n is 0-12. 
wherein
R3 and Y have the meanings given above;
R7 and R8 are identical or different and are hydrogen, C1-6alkyl, C6-10aryl, (C6-10)aryl-(C1-6)alkyl or (C1-6)alkyl-(C6-10)aryl, it being possible for the alkyl and/or aryl radicals to be substituted by hydroxyl, C1-6alkoxy, C6-10aryloxy or halogen; and
m and n are 0-12: 
wherein each R1, independently, has the meaning given above; Z is hydrogen or halogen; and n is 1 or 2. 
wherein n is 0-12. 
wherein m and n are 0-12. 
wherein R3 has the meaning given above; and n is 0-12. 
wherein R7 and R8 have meanings given above; and m and n are 0-12. 
wherein R7 and R8 have meanings given above; and m, n and p are 0-12.
The dyes with structures (I) to (IX) are, in part, novel compounds and can be prepared in accordance with well known processes. More particularly, dyes of structure (II) in which n is not zero or 2, all dyes of structures (III) and (V), dyes of structure (VI) in which m and n are not zero, 2 or 6, dyes of structure (VIII) in which m and nxe2x89xa01, all dyes with structures (VII) and (IX) are novel. The processes for their preparation are as follows:
The corresponding dicarboxylic or tetracarboxylic acid anhydrides of the formulae 
are condensed with the corresponding alkylene diamines
H2Nxe2x80x94(CH2)xe2x80x94NH2xe2x80x83xe2x80x83(X)
or 
and optionally further reacted resp. first reacted with an appropriate phenylene diamine 
The respective reaction conditions can be chosen e.g. as in the preparation examples A to F.
Appropriately, the protective colloid solution in water is prepared separately with the concentration of water-soluble polymer being between 0.2 and 1%, preferably 0.4-0.7%. Typical representatives of this class of compounds are hydroxyethylcellulose, sodium salt of carboxymethylcellulose, methylcellulose, ethylcellulose, polyvinyl alcohol, and water-soluble polymers and copolymers of acrylic or methacrylic acid. The protective colloid is used in an amount of 5-30 parts by weight, preferably 12-20 parts by weight, per 100 parts by weight of prepolymer.
The dyed soluble and fusible prepolymer is transformed to the insoluble and infusible hardened resin by slowly adding with high shear (6000-7000 rpm with a Homomixer) the prepolymer-organic solvent mixture to an aqueous solution of protective colloid containing either no surfactants or a non-ionic surfactant or a mixture of non-ionic and ionic surfactants and an acidic curing catalyst at a reaction temperature in the range from 70-100xc2x0 C. Appropriate non-ionic surfactants are Solsperse 41090 (Phosphated alkoxylated polymer from ZENECA Specialties), Surfinol CT-111 (2,4,7,9-tetramethyl-5-decyn-4,7-diol from Air Product and Chemicals, Inc.) and Triton CF-10 (Alkylarylpolyether from Union Carbide). Examples of a mixture of non-ionic and ionic surfactants are the compositions of the above mentioned non-ionic surfactants and potassium tripolyphosphate, sodium lauryl sulfate or Surfinol CT-131 (from Air Product and Chemical, Inc.) in a ratio of 2-3 parts by weight of non-ionic and 1-2 parts by weight of ionic surfactant. These surfactants are effectively used in an amount in the range of 5-15 parts, preferably 8-12 parts by weight per 100 parts by weight of prepolymer. Appropriate curing catalysts are mineral acids such as hydrochloric, sulphuric and phosphoric acids, sulfonic acids such as benzenesulfonic, toluenesulfonic and dodecylbenzenesulfonic acids, organic acids such as phtalic, benzoic, oxalic and sulfamic acid. These acids are effectively used in an amount in the range of 0.1-5 parts, and preferably about 1-2 parts by weight per 100 parts by weight of prepolymer. The rate of adding the prepolymer-organic solvent mixture, as well as the temperature range of protective colloid solution is selected preferably so that the complete and fast evaporation of low-boiling point solvent from the said mixture can be achieved. In the case where acetone (b.p. 56xc2x0 C.) or methanol (b.p. 65xc2x0 C.) are used the temperature range of 70-85xc2x0 C. is recommended. In the case where methylethylketone (b.p. 79xc2x0 C.) or ethanol (b.p. 78xc2x0 C.) are used the temperature range of 85-100xc2x0 C. is recommended. There is a tendency that the particle shape of the resulting fine particles is changing from spherical to non-regular as the temperature of protective colloid solution is increased and the concentration of surfactants is decreased. In preparing an aqueous suspension of insoluble and infusible hardened resin, it is necessary to hold the temperature in the range of 70-100xc2x0 C. for at least 1 hour, and preferably 2-4 hours with a continuing agitation with a Homomixer. When the hardening of the prepolymer is carried out in a short time of less than 1 hour or with no agitation, partial or total aggregation of the soluble and fusible resin is observed with the result of the formation of large particles or lumps in addition to the finely divided particles.
If no surfactants are present or a low concentration of surfactants (below 8 parts by weight per 100 parts of prepolymer) is used, a finely divided hardened resin is obtained by separating from the suspension and drying the resin with heating at a temperature ranging from 60 to 150xc2x0 C. for about 2 to 10 hours and thereafter crushing the aggregates by means of a pin mill or jet mill. If a sufficient concentration of surfactants (higher than 8 parts by weight per 100 parts of prepolymer) is used, two main fractions of product can be obtained by filtration:
1. Up to 70-80% of the material is a stable (at least for 3-4 months) aqueous suspension of submicron particles: up to 70% below 0.7 microns and up to 40% below 0.5 microns. After an additional treatment, this suspension can be used in a wide range of applications, including the ink-jet inks.
2. Up to 20-30% of the material can be obtained as a dry powder by separating from the suspension and treating according to the same procedure as for material obtained with no surfactants present.
The resulting resin obtained by the invention process demonstrates extremely superior opacity, dispersibility, heat resistance and resistance to solvents when used as a pigment. Hence, the vividness and staining power of the dye used can be manifested effectively, the finely divided hardened resin of this invention can be used effectively in a very wide range of application.